Re: [APML] OT: 240 Galaxies in 3 square degrees of Virgo

["Chris Cook" <ccook@cape.com>]

If you are using a 10D,20D or 300/350D w/o their respective battery grips, I
doubt you will run into problems because of weight.  The 1DMk2 is heavier
than just a 20D/Rebel type body by itself.

The 1DMk2 weighs 55.2oz, a 20D is 27.2oz and a 350D/Rebel is only 19oz.

Chris

-----------------------------
Chris Cook Photography
www.cookphoto.com


----- Original Message ----- 
From: "Don Westergren" <westergren@nethere.com>
To: "Discussion of Film Astrophotography" <astro-photo@seds.org>
Sent: Monday, April 18, 2005 8:29 PM
Subject: Re: [APML] OT: 240 Galaxies in 3 square degrees of Virgo


> Hi Jerry,
>
> If your camera was set with the upper left corner of the FOV either up or
> down, the adapter could let the camera tilt and cause local distortion.
It
> all depends on your local hour angle, but that would confirm your
> hypothesis.
>
> I wondered about it because I'm about to start using a DSLR, and they are
> more sensitive to star distortions than film.  I'm also using an AP
> refractor (180f9) and don't know if I will need to use a flat field lens
as
> well.
>
> Don
>
> > Hi Don,
> >
> > I don't know for sure what's causing the elongated stars in the upper
> > left, but I have a guess...  It's  not field rotation for sure, I spent
an
> > hour drift aligning and the exposures were only 7.5 minutes.  It's not
> > atmospheric differential refraction.
> >
> > I think it's astigmatism because the camera's focal plane was not
> > perfectly coincident with the focal plane of the scope.  The camera is
> > very heavy and I have an Astro-Physics 2 inch adapter with EOS T-mount.
> > There is a LOT of slop and play in the EOS T-mount adapter the AP is
> > using, and I just think the weight of the camera pulled that corner
down.
> >
> > At least that's my guess right now.
> >
> > The AP adapter also vignettes, even with the smaller size chip than a
> > piece of 35mm film, so I'm looking for other solutions to this problem
> > right now.
> >
> > Jerry
> >
>
>
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>
>


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